In the fluorescent lamp art, both preheat type lamps and rapid-start type lamps are commonly encountered. In the preheat type of discharge lamp, heater current flows through the electrodes only during lamp ignition. Thereafter, it is a common practice to provide an external voltage sensitive starter which opens the heater current circuit discontinuing heater current flow. In contrast, a rapid-start type fluorescent lamp normally has a constant heater current flow through each electrode both during ignition and during operation of the lamp. Unfortunately, heater current flow during operation of a rapid-start fluorescent lamp is lost power which obviously reduces efficiency of the discharge lamp.
Numerous suggestions have been made for enhancing the efficiency of rapid-start fluorescent lamps. For example, U.S. Pat. Nos. 4,052,687; 4,097,779; 4,114,968; 4,156,831 and 4,171,519, all assigned to the Assignee of the present Application, suggest numerous configurations for enhanced operation of rapid-start fluorescent lamps. Generally, each provides a thermally responsive circuit breaker suitable for use in discontinuing heater current when the fluorescent lamp becomes operational.
Although each of the above-listed structures and techniques provides discharge lamps having numerous advantages over prior known configurations and processes, it has been found that problems remain. More specifically, it has been found that a configuration wherein a separate capsule containing a circuit breaker arrangement, which is attached to the inner leads of a fluorescent lamp, does present problems. For instance, attaching a separate capsule containing a circuit breaker requires a cut-out of the inner lead of the discharge device. However, severing the inner lead to facilitate this addition tends to undesirably weaken the support structure for the attached electrode which is obviously an undesirable result. Also, a separate apparatus is required to fabricate a separate capsule and a separate feed system must be utilized to add the capsule to the lamp fabrication operation.